Japanese Laid-open Patent Publication No. 2015-178438 describes the provision of a gallium nitride freestanding substrate that has favorable crystallinity and is capable of forming high-quality semiconductor device structures. As gallium nitride crystals approach perfect crystals, an abnormal transmission phenomenon occurs where X rays pass through the crystals with no attenuation due to the absorption coefficient for X-rays being exhibited, so that by using this and using a transmitted X-ray topography as a test item, it is possible to detect unacceptable defects in the testing (inspection) process.
Japanese Laid-open Patent Publication No. 2014-189484 describes how it is difficult to form a high-quality epitaxial layer with extremely few crystal defects on a substrate due to crystal defects in the surface of an SiC monocrystalline substrate propagating to the epitaxial layer or due to disturbances in the crystal structure to the defect-free portions inside the substrate. The method for manufacturing a silicon carbide semiconductor substrate disclosed in this document includes: a defect position identifying step that identifies positions of crystal defects formed in a silicon carbide semiconductor substrate by X-ray topography or photoluminescence; a crystal defect nullifying step that performs a nullifying process which suppresses propagation of crystal defects to the epitaxial layer by irradiating the identified regions of the crystal defects with a particle beam; and an epitaxial layer forming step that forms an epitaxial layer on the substrate that has been subjected to the nullifying process.
Japanese Laid-open Patent Publication No. 2014-2104 discloses the provision of a method of evaluating a SiC monocrystalline substrate that can evaluate the dislocation density of the SiC monocrystalline substrate via reflection X-ray topography without using a monochromator. The method of evaluating an SiC monocrystalline substrate in this document evaluates dislocation in the SiC monocrystalline substrate using reflection X-ray topography and is characterized by obtaining an X-ray topography image of the SiC monocrystalline substrate using MoKα rays as the X-ray source and an asymmetric reflective surface as the diffraction surface, and by measuring the dislocation density of the SiC monocrystalline substrate using the X-ray topography image.